1. Field of the Invention
The present invention relates to a method and a device for time and/or temperature determination, and more specifically to a method for monitoring the handling conditions of at least one object, such as an individual package or a stack of such packages containing refrigerated or frozen products, the object being intended to be handled under certain predetermined conditions, and to a device for carrying out the method.
2. Description of The Related Art
The term "handling" as used in the present context relates to storage, transport and similar treatment of an object, and the expressions "handling conditions" and "conditions" as used in the present context relate to either the temperature prevailing during the handling of the object, or the time and the temperature, i.e. the total or integrated influence of time and temperature on the object during the handling thereof.
There are a great many objects and products, such as foodstuffs, medicines, vaccines, blood products, photographical film etc, that are temperature-sensitive and should be stored or handled at a certain temperature in order to prevent quality degradation. Typical examples of such products are foodstuffs, such as refrigerated foods, e.g. milk, vegetables etc, or frozen foods, e.g. meat, fish, ice-cream etc. For example, in order that a deep-frozen product should have a satisfactory quality when reaching the shop, it should not be subjected to a temperature exceeding e.g. about -15.degree. C. to -18.degree. C., after departure from the producer and until the time of arrival in the shop. For refrigerated foods, the corresponding temperature is about +4.degree.-8.degree. C. On its way from the producer to the consumer, a frozen food passes through a large number of handling steps, such as storage with the producer, transportation from the producer to the wholesaler, storage with the wholesaler, transportation from the wholesaler to the retailer, and storage with the retailer. In all these partial steps, the deep-frozen food must be handled correctly, i.e. at a temperature which does not exceed about -15.degree. C. to -18.degree. C., in order to prevent its quality from degrading. To this end, the temperature of the product is checked at regular intervals in each partial step, i.e. during transport and storage.
One way of performing such checking is to insert a needle-equipped electronic thermometer into a stack of packages containing deep-frozen products, and to read the temperature on the thermometer. However, this involves several disadvantages. First, the electronic thermometer is expensive to manufacture and purchase, and requires for its operation batteries which must be replaced at regular intervals. Moreover, the thermometer must be calibrated for correct indication, and the thermometer needle must on each measuring occasion be held inserted in the stack of packages with frozen products for several minutes to enable the thermometer to adjust itself and display the correct temperature. As deep-frozen products, especially foods, are normally stacked on pallets and at least one check must be made on the products on each pallet, it is understood that the total time for checking e.g. the load on a long-distance truck or in a storeroom is quite considerable and thus involves substantial costs.
There is thus a need to make the observation quicker and less expensive, and preferably also to make possible subsequent observation of the handling of the product to ensure that this handling falls within the limits applying to the product concerned, in respect of its consumability. This is also important in view of the strict products liability currently incumbent upon manufacturers in most countries.
The present invention aims to achieve this and obviate the shortcomings inherent in the prior-art technique, by means of a device which is easy and inexpensive to manufacture and which constantly is at the temperature of the product concerned, to enable a quick temperature observation without any delay for temperature adjustment of the device.
If one wishes to perform a more complete observation of the handling conditions of a product, and thus of its quality, it is further possible according to the invention, instead of only checking the temperature, also to check both temperature and time, more specifically by making an integration of the temperature conditions to which the product is subjected over the time during which the handling of the product takes place.